(1) Field of the Invention
This invention relates to a method of producing a sintered hard metal with a diamond film, and more particularly to a method of producing a sintered hard metal with a diamond film suitable for, for example, various cutting tools such as bits, end mils, drills, and cutters, draw dies, blanking dies, abrasion resistant machine parts, and the like.
(2) Description of the Related Art
Conventionally, in the field of various cutting tools such as bits, end mils, and cutters, since cutting tools excellent abrasion resistance can be obtained by using a diamond film as a protective film for cutting tools made of a sintered hard metal, the demand for cutting tools made of a sintered hard metal on which a diamond film is formed is increasing.
Conventionally, as methods of forming a diamond film on a sintered hard metal have been suggested, for example, a method wherein, prior to the formation of a diamond film, a sintered hard metal is subjected to ion etching treatment thereby activating the surface of the sintered hard metal, and then the sintered hard metal is contacted with an activated raw material gas (see Japanese Laid-Open Patent Application No. 204695/1985), and a method wherein prior to the formation of a diamond film on a substrate of a cermet, the cermet is etched with an acid solution to remove the bonding phase of the surface, and then the cermet is contacted with an activated raw material gas (see Japanese Laid-Open Patent Application No. 52363/1986).
However, the cutting tools of a sintered hard metal formed with a diamond film that are obtained by these methods still are accompanied by such problems that the cutting edge is still abraded, that chipping (breaking part of the cutting edge) will occur, and that it is still hardly said that the adhesion of the diamond film is satisfactory.
Thus, generally the adhesion between the surface of a sintered hard metal and a diamond film is poor.
Therefore, in order to improve the adhesion between the surface of a sintered hard metal and diamond, techniques for forming an intermediate layer between a sintered hard metal and a diamond thin film are developed.
For example, Japanese Laid-Open Patent Application No. 126972/1983 discloses a method wherein after an intermediate layer made of one or more compounds selected from a carbide, a nitride, a boride, and an oxide of a metal of Groups IVa, Va, and VIa of the periodic table is first formed on the surface of a sintered hard metal, a diamond thin film is formed on the intermediate layer.
Also, Japanese Laid-Open Patent Application No. 159981/1984 discloses a tool that includes on a metal such as W, Nb, Ta, V, Cr, and Hf a diamond thin film formed by the CVD method or the like.
However, in either of the above Patent Applications, since the thin film is formed stepwise by forming first an intermediate layer and then the diamond thin film, it is hardly said that the adhesion between the sintered hard metal and the diamond thin film has been improved sufficiently enough to the practical level although the methods are allegedly intended to improve the adhesion.
Further, as a tool member coated with artificial diamond, a tool member coated with artificial diamond is suggested wherein at least the tool working surface of a cermet substrate member is coated with an artificial diamond film having an average layer thickness of 1 to 1.2 .mu.m formed by an artificial diamond deposition formation process via a deposited layer having an average layer thickness of 0.05 to 1.2 .mu.m made of any one of W, Mo, and Nb and their alloys [see Japanese Patent Publication No. 15347/1988 (Japanese Laid-Open Patent Application No. 208473/1985)].
However, since, in the method disclosed in the Japanese Patent Publication mentioned above, the composition of the reactant mixed gas for the formation of diamond is 1 vol. % or below, the deposited metal layer is not effectively carbonized. Therefore, the adhesion between the diamond layer and the cermet substrate member is accordingly poor.